Rotation sensors using an MR (magnetoresistor) element or a Hall element are known in the prior art. A rotation sensor has an internal circuit, which performs signal processing to output a pulse signal at a frequency proportional to the rotation speed of a rotor, which is the subject of detection.
A rotation sensor such as the rotation sensor described in Japanese Laid-Open Patent Publication No. 2001-165951 generates two types of pulse signals having different forms as pulse signals representing the rotation speed of a rotor. When the rotation speed of the rotor is low, the two types of pulse signals are used as an information signal showing the rotation direction through the difference in the forms. When the rotation speed of the rotor is high, the two types of pulse signals are separated by using one of the pulse signals as “0” information and the other one of the pulse signals as “1” information so that circuit failure diagnosis information and other information are used as a binary information signal.
Japanese Laid-Open Patent Publication No. 10-70524 describes a rotation sensor that digitizes different information for the rotation speed and rotation direction of a rotor. The digitized information superimposes between pulses, which are output at a frequency proportional to the rotation speed of the rotor, a different pulse train. Accordingly, the pulse train is used as an information signal showing different information for the rotation speed and rotation direction of the rotor.
In the rotation sensor of Japanese Laid-Open Patent Publication No. 2001-165951, selective information acquisition corresponding to the rotation speed (low speed, high speed) of the rotor, which is the detection subject, is necessary. Thus, one of the foregoing cannot be constantly monitored. Further, the output of the signal representing different information of the rotation speed and rotation direction of the rotor is dependent on the frequency of the pulse signal. Thus, it is difficult to obtain a stable information transmission speed (communication speed).
In the rotation sensor of Japanese Laid-Open Patent Publication No. 10-70524, the period during which the pulse train representing information can be superimposed is limited to the period between pulses, which are output at a frequency proportional to the rotation speed of the rotor. Accordingly, when the rotation speed of the rotor is high and the period between pulses is short, the pulse train representing information cannot be output.